Crystal-controlled calibrator



June 12, 1928.

R. B. OWENS CRYSTAL CONTROLLED CALIBRATOR Filed June 1927 INVEN TOR.

ATTORNEY Patented June 12, Q28.

UNITED STATES- PATENT OFFlCE.

RAYMOND B. OWENS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIREDBADIO, IN 0., OF NEW YORK, N. Y. A CORPORATION OF DELAWARE.

CRYSTAL-CONTROLLED GALIBRATOB.

Application filed June 8, 1927. Serial No. 197,495.

My invention relates broadly to piezo electric crystal control circuitsand more particularly to a calibrator apparatus depending for itsoperation upon the natural frequency characteristics of piezo electricdevices.

One of the ;objects of my invention is to provide a practical circuitarrangement for deriving from a piezo electric device a plurality ofharmonic frequencies which, by reason of their constant frequencycharacteristics, may be employed in accurately calibrating associatedelectrical circuits.

Another object of my invention is to provide a circuit system for acrystal calibrator comprising an electron tube oscillator cir cuit, adetector and an amplification system by which harmonic frequencies maybe selected from a piezo electric device and sustained by saidoscillator circuit.

Still another object of my invention is to provide a piezo electriccrystal controlled electron tube oscillator system in which the outputcircuit of the oscillator has a large ratio of inductance to capacityfor the development of harmonic frequencies from said piezo electriccrystal.

My invention will be more fully understood from the specificationhereinafter following by reference to the accompanying drawings wherein:

Figures 1 and 2 show curves illustrating opposite conditions that mayexist in the relation of impedance and frequency in an electricalcircuit upon which phenomena my invention is based; Fig. 3 illustratesone embodiment of the crystal calibrator circuit arrangement of myinvention; and Fig. 4 illustrates a modified wiring arrangement for thecrystal calibrator in which a parallel feed circuit is, applied to thecrystal controlled oscillator system.

The crystal calibrator of my invention is a crystal controlledoscillating circuit which isso designed as to reenforce the strength oftheharmonic frequenciesof the fundamental of the crystal that aredeveloped in e the plate circuit of this oscillator. My experience withcrystal oscillating circuits has shown that when the ratio of theinductance to the capacit. used for tuning the plate circuit to pro acethe oscillating condition is small, the harmonic frequency currents inthis circuit are very weak, and it is very vhard. to. observe anyharmonic frequency the fact that a circuit having a small inductance tocapacity ratio has a maximum lmpedance at one definite frequency and arapidly diminishing impedance above or below this frequency, while ifthe ratio is increased, the resonance is less pronounced and if theratio is made large enough, the impedance curve will be fairly uniformover a large range of frequencies. Now it is known that the maximumtransfer of power from one circuit to another is obtained when theimpedances of the circuits are identical, and for this reason and by theuse of the large inductance and very small capacity for the plate load,a condition arises where the tube impedance may be matched with the lateload impedance for a wide range of requencies. 1

Figs. 1 and 2 show thev values of impedance that can be had with the twoextreme cases that have been previously discussed. Fig. l isa curveshowing relation of impedance to frequency for a circuit having a smallinductance and a large capacity; while Fig. 2 represents the conditionobtained with a pancake or universal coil that has a large sary toprovide a detector and amplifier sys tem that will respond to allfrequencies without resort to the use of a number of tuned circuits. Toaccomplish this result I employ a coupling coil that is similar inimpedance characteristics to that of the plate coil system of theoscillator and connect this coil through a grid leak and condenser tothe grid and filament of the detector tube as shown in Fi 3.

To use this calibrator as a frequency.-

standard, it is necessary to employ a coupling wire, shown as C in Fig.3, and place this close to the radio frequency generator whose frequencyis to be measured. This wire will pick up a weak signal fromthetransmitter that will combine with one of the harmonic frequencies ofthe calibrator and produce a beat note in the plate circuit of thedetector tube. This beat note is am lified by use of one or two stagesof ampli cation as shown in Fig. 3.

Referrin to "the drawings in more detail, reference c aracter 1designates an electron tube arranged as an oscillator. 4 The electrontube 1 includes filament electrode 1, grid electrode 1 and plateelect-rode 1. The filament electrode 1 is heated from battery system 9.An input circuit 2 is provided for the electron tube 1 to which is alsoconnected the output circuit 3. The input circuit 2 includes piezoelectric crystal element 4 that is positioned between electrodes 4 and4" L O which connect respectively with grid electrode 1 and filamentelectrode 1*. A proper biasing potential is supplied to the gridelectrode 1 by the arrangement of resistor 5 across the electrodes 1 and1 The output circuit 3 includes a large inductance 6 havin a smalldistributed capacity and providing a low impedance matched with respectto the tube impedance. The inductance 6 is arranged "in circuit withbattery 7 that is shunted by means of by-pass condenser 8. Inductance 6is designed to have a large inductance to capacity ratio. Thisinductance is coupled to a corresponding inductance 10 disposed in theinput circuit of a detector tube 12. The detector tube 12 includesfilament electrode 12*, grid electrode 12 and plate electrode 12-. Thepick-up wire, Cconnects to the rid circuit of the de-' tector tube. Thegrit? leak and grid condenser 11 is shOWn disposed in the grid circuitof tub tube 12. Filament electrode 12 is heated from battery 20. Theoutput circuit of tube 12 includes the primary winding 15 of an audiofrequency transformer system 14 and the battery system 19. The secondarywindin 16 of the transformer 14 connects to the input circuit of theaudio frequency amplifier tube 17. The amplifier tube 17 includesfilament electrode 17,- rid electrode 17' and plate electrode 17.att/ery 21 is arranged to supply the high potential to the outputcircuit of amplifier tube 17. Telephone receivers 18 are arranged in theoutput circuit of the amplifier 17. While only a single stage of audiofrequency amplification has been illustrated, it will be understood thatadditional stages of amplification may be employed.

In Fig. 4, I have shown the oscillator circuit provided with a parallelfeed system in the output thereof. The output circuit 3 includes a choke23 and a battery system 24.

A high frequencybranch circuit 26 is connected around the power supplycircuit and includes condenser 25 and the inductance 6 having a largevalue of inductance and small distributed capacity as heretoforeexplained in connection with Fig. 3. The high frequency oscillations,occurring in the circuit whose .frequency is to be measured, are pickedup by means of the coupling wire 0. The oscillations of unknownfrequency combine with one of the harmonic frequencies produced by theoscillator system including piezo electric crystal element 4 andinductance 6 for deriving a beat note in the plate circuit of thedetector tube 12. The beat note may be amplified to any suitable numberof stages of amplification for operating the telephones 18.

The inductances the pancake or universal type which, by their inherentconstruction, enable a high ratio to be obtained. A. wide variety ofharmonics may be derived in this manner enabling a reading to be securedwith respect to the frequency of the circuit under observation.

While I have described my invention in one of its preferred embodiments,I desire that it be understood that modifications may be made and thatno limitations upon my invention are intended other than are imposed bythe scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A crystal calibrator circuit comprising an electron tube oscillatorincluding input and output circuits, a piezo electric crystal elementconnected in said input circuit and means in said output circuit havinga large inductance to capacity ratio for the derivation of harmonicfrequencies from said piezo electric crystal element, and means fordetecting the individual harmonic frequencies derived from said piezoelectric crystal element.

2. A crystal calibrator circuit comprising an electron tube oscillatorhavinginput and. output circuits, 2. piezo electric crystal elementconnected in said input circuit and a coil connected to said outputcircuit, said coil having a relatively large value of inductance and arelatively small distributed capacity for the derivation of harmonicfrequencies from said piezo electric crystal element.

3. A piezo electric crystal contr'olled calibrator including anoscillator, a detector, and a signal observing circuit, a piezo electriccrystal element, connections between said piezo electric crystal elementand said oscilator, and means interposed between said oscillator andsaid detector for deriving a plurality of harmonic frequencies from said6 and 10 are preferably of piezo electric crystal element and fortransferring the effects thereof to said signal observing circuit.

4. In a piezo electric crystal controlled calibrator system, thecombination of an oscillator circuit, a detector, and a signal observingcircuit, a piezo electric crystal element connected with saidoscillator, an inductively coupled circuit interposed between saidoscillator and said detector, said inductively coupled circuit beingconstituted by coils having large inductance and relatively smalldistributed capacity for the development of harmonic frequencies fromsaid piezo electric crystal element and the impression of such harmonicfrequencies upon said signal observing circuit.

5. A piezo electric crystal calibrator system comprising an electrontube oscillator including input and output circuits, a piezo electriccrystal element disposed in said input circuit, a coil having arelatively large value of inductance and a relatively small distributedcapacity arranged in said output circuit, a detector, a coil connectedin circuit with said detector and coupled with said aforen'ientionedcoil, a coupling wire extending from said detector for collecting andtransferring to said detector high frequency oscillations, and a signalobserving circuit connected to said detector for rendering apparent abeat frequency formed by the combination of harmonic frequencies derivedfrom said piezo electric crystal element and the high frequencyoscillations collected by said coupling wire.

6. A crystal controlled calibrator system, an electron tube oscillatorincluding input and output circuits, an electron tube detector includinginput and output circuits, a signal observing circuit connected to theoutput circuit of said detector, a coupling wire connected to the inputcircuit of said detector, a piezo electric crystal element connected tothe input circuit of said electron tube oscillator, and means couplingthe output circuit of said oscillator with the input circuit of saiddetector for transferring to said detector a plurality of harmonicfrequencies derived from said piezo electric crystal element and meansfor impressing high frequency oscillations collected by said couplingwire upon said electron tube detector, whereby the combined effects ofharmonic frequencies derived from said piezo electric crystal elementand the high frequency oscillations collected by said couplin wire maybe impressed upon said signa observing circuit.

RAYMOND B. OWENS.

